1. Field of the Invention
The present invention relates to a printing apparatus having a so-called “double-sided printing” function.
2. Related Art
According to a Japanese Patent Publication No. Hei. 7-237336, which is incorporated herein by reference, there is provided a conventional double-sided printing system which uses two (2) printers for printing on both faces of a continuous paper. An intermediate buffer device absorbing the paper feed speed difference between first and second printers is provided between the first and second printers, and a residence quantity detector detects residence quantity of the continuous paper in the intermediate buffer device. The conventional double-sided printing system is controlled as follows: the printing and paper transporting by the second printer is stopped when the residence quantity becomes a first set value or less, and the printing and paper transporting by the first printer is stopped when the residence quantity becomes a second set value or more.
However, since the conventional double-sided printing system has the intermediate buffer device, the transportation path of the continuous paper between the first and second printers tends to be long and complex. As shown in FIG. 4, since there is also provided an overturning unit 61 to and from which the continuous paper is fed at an angle, the continuous paper 63 past the unit 61 can easily bend in the inclination direction. The passing position of the continuous paper through the unit 61 can be shifted to the left or right of the central passing position, so that edges of the continuous paper 63 can be torn off which causes jamming.
According to the conventional printing system including the intermediate buffer, since the continuous paper must be transported as it is until the double-sided printing is completed, it is required to have a plurality devices, such as the intermediate buffer, for controlling transportation of the continuous paper. Therefore, total cost is increased. This is the first task of the present invention.
In general, a roll paper as a continuous paper can be used as a recording medium for printing of a conventional recording apparatus, such as a facsimile or a printer. The roll paper is useful in that it can be used for a continuous long-range printing job and proper for multiple-size printing function.
On the other hand, in case of the roll paper, the roll paper must be cut at a desired position after a printing job is completed. In case the roll paper is manually cut, the cutting process requires human labor and edge profile is not desirable. So, in some conventional recording apparatus, an automatic cutting device is installed to perform the cutting job automatically.
When the above described cutting device is installed on the conventional recording apparatus, unnecessary cutting dust is generated. Then, a dust stacker is additionally installed under the cutting device to gather the cutting dust. In this case, the dust stacker needs to be discarded after some time. However, if the user leaves alone the dust stacker without discarding it, the cutting dust in the dust stacker can flow over to give bad effects to the recording apparatus. Further, this problem is not only in the case of continuous paper but also in the case of discrete paper which is cut at a predetermined position. This is the second task of the present invention.
Further, as the roll paper becomes longer, or as unit weight of the roll paper increases, total weight of one roll paper also increases. As the total weight of the roll paper increases, the forces required to feed the roll paper also must be increased. The roll paper of increased weight has increased transporting load (or transportation load), so that paper transporting precision of a transporting roller or a sheet feed roller, which transports the continuous paper at a predetermined pitch, toward the recording unit is degraded, and the printing quality is also degraded. This is the third task of the present invention.
The transporting device of the conventional recording apparatus has a recording medium nipped between a transporting roller and a slave transporting roller, and transporting of the recording medium is performed by rotating the transporting roller. Here, the nipping of the recording medium between the transporting roller and slave transporting roller has an important role because the recording medium is fed by being nipped and the transporting position of the recording medium is also governed by the nipping between the transporting roller and the slave transporting roller.
The firm nipping of the recording medium between the transporting roller and the slave transporting roller may be embodied by a roller pressing device which provides pressing forces to either or both of the two (2) transporting rollers to make them closely contact with each other. The roller pressing device, the transporting roller and the slave transporting roller comprise a transporting device, which is removably installed on the recording apparatus. In this case, since the transporting roller and the slave transporting roller are closely contacted with each other by the roller pressing device, a user much first make sure that the recording medium is nipped between the transporting roller and the slave transporting roller, and then install the transporting device on the recording apparatus.
However, the nipping job done by a user is not only complex and troublesome, but also incomplete. Therefore, when the transporting device is dismantled from the recording apparatus, it is greatly desirable that the transporting roller and the slave transporting roller may not be closely contacted with each other and that the recording medium may be simply put in between the two (2) transporting rollers. Further, it is also desirable that when the transporting device is installed on the recording apparatus, the roller pressing device is automatically moved to provide the pressing force to the transporting rollers for the recording medium to be nipped between the transporting roller and the slave transporting roller. To sum up, by making the recording medium nipping job simple, manipulatability of the transporting device can be increased. Further, the above description is applied not only to a transporting device which transporting device which transports a continuous paper or a discrete paper, but also to a roll paper cassette for setting a roll type recording medium (the fourth task of the present invention).